A fast resistance measurement system for impedance tomography using a bipolar DC pulse method

A bipolar pulse DC resistance measurement modified for use in electrical im pedance tomography is presented. The measurement method compensates for off set voltages. which usually exist between electrodes. The absence of phase shifts as encountered in AC systems using sinusoidal excitation greatly sim plifies the measurement. For low to medium resistivity of the subject the m ethod is faster than AC methods. Measurements on an equivalent four-termina l network show repeatabilities of approximately 0.01%. The method is applie d in a PC-controlled system with 192 electrodes to measure fluid distributi on in porous rock samples during petrophysical experiments. Repeatability o f acquired data sets is typically 4 to 5 LSB of a 16-bit A/D converter. com pared with 2 to 3 LSB obtained from a four-terminal network, and allows rel iable reconstruction.